1. Field of the Invention
This invention relates to a cuff pressure regulator for an endotracheal-tube cuff.
2. Related Art Statement
Heretofore, in artificial ventilation under general anesthesia or through a tracheotomy, there has been used a cuffed endotracheal-tube for intubation and tracheotomy to prevent a leakage of anesthetic gas, oxygen or air toward the outside and to prevent the inflowing of vomitus from the esophagus into the trachea. In the cuffed endotracheal-tube, if the cuff is brought into contact with the inner wall of the trachea under high pressure, normal blood flow in the mucosa is disturbed due to excess pressure for capillary vessels at the contact portion, and there occurs a dysfunction of said tunica mucosa (ciliary epithelium) so that, in an extreme case, such contact portion becomes necrotic.
Contrary to this, if the cuff is brought into contact with the inner wall of the trachea under too low a pressure, the artificial respiration can be inhibited due to a leakage of anesthetic gas, oxygen or air, and the vomitus is allowed to flow into the lungs from the esophagus. Therefore, in the cuffed endotracheal-tube, it is necessary to maintain the cuff contact pressure on the inner wall of the trachea at a suitable level such that neither gas supplied from an anesthesia machine or a respirator leaks nor blood flow in the capillaries at the contact portion is disturbed.
In the Japanese Utility Model Publication No. 7,742/85, there has been proposed an apparatus for controlling the cuff pressure wherein, on the basis of Pascal theory, pressure in a small vessel connected to the cuff, i.e., the inner pressure of the cuff, can be maintained at a desired level by changing the weight or the amount of liquid in a bottle on a bellows or a cylinder arranged movably up and down in the vessel.
Further, in Japanese Journal of Medical Instrumentation vol. 51, Suppl., 1981, pp. 190-192 "72. Apparatus for controlling cuff pressure during nitrous oxide-oxygen anesthesia" and a society magazine of "Sapporo Ishi" (Medical Journal) 50(5). 1981. pp. 363-371 titled "Changes in Intra- and Lateral-Cuff Pressure during Nitrous Oxide Anesthesia and Clinical Evaluation of a New Cuff Pressure Regulator", there has been proposed a cuff pressure regulator for keeping the cuff inner pressure at a constant level by introducing air through a filter by operation of a diaphragm pump, supplying the thus introduced compressed air to a Y-connector through a pressure-reducing valve under a predetermined pressure higher than the cuff maximum pressure, connecting one output end of the Y-connector to the cuff, connecting the other output end of the Y-connector to the ambient through an adjustable orifice and controlling the discharge amount of surplus air by said orifice.
However, in the former cuff pressure regulator mentioned above, since the desired cuff pressure is achieved by changing the weight of or the amount of liquid in a bottle arranged on the bellows or the cylinder, it is necessary to select one among many weights, each having a different weight, or to adjust the amount of said liquid to obtain a desired weight. Therefore, there is a drawback in that it is very cumbersome to achieve such adjustment. Moreover, in order to have the weight exactly correspond to the cuff pressure when using the bellows it is necessary to make the dynamic resistance of the bellow extremely small and to manufacture it uniformly, and when using the cylinder it is necessary to move the cylinder airtightly with no resistance against the vessel wall. Therefore, in both cases, there is a drawback in that it is very difficult to manufacture the cuff pressure regulator in an easily operable and inexpensive manner. Further, since the cuff pressure is obtained by the weight, the cuff pressure can not be achieved effectively if the cuff pressure regulator falls or is laid down. In addition, in an extreme case of such falling down or being laid down, the cuff pressure is abruptly decreased and becomes even negative, so that the patient during operation under anesthesia may fall into a dangerous condition. Still it is impossible to correct such disturbed situation from the outside of an isolated space such as a hyperbaric chamber.
In the latter cuff pressure regulator mentioned above, since the cuff pressure is adjusted by controlling the discharge of the surplus air (having a predetermined pressure set fixedly above the cuff maximum pressure) through an adjustable orifice toward the external environment by using the adjustable orifice, there is a drawback that it is very difficult to achieve a fine adjustment of the cuff pressure. Moreover, since the pressurized air is suplied to the cuff through the pressure-reducing valve by operating the diaphragm pump by means of an electric motor, the cuff pressure is pulsating due to the motion of said diaphragm pump, and the cuff pressure is abruptly decreased to the atmospheric pressure if the power supply is accidentally interrupted, so that the patients can be endangered. Further, since said pump pressure usually becomes too low and also because it is necessary to prohibit an installation of an electric motor etc. in a hyperbaric oxygen chamber for the sake of safety, there occurs a drawback in that a cuff pressure regulator of this type can not be used for hyperbaric oxygen treatment.
When a cuff filled with a gas such as oxygen is used in a hyper- (or hypo-) baric chamber and the like, the cuff volume increases (or decreases) corresponding to a decrease (or an increase) of relative cuff pressure due to an abrupt change of the environmental pressure. Therefore, it is necessary to maintain the cuff contact pressure against the trachea wall without variation of the cuff volume. To this end, water is widely used instead of gas for this purpose. However, since it is almost impossible to adjust precisely the cuff contact pressure against the trachea inner wall when water or liquid is used to inflate the cuff instead of gas, there likely occur serious complications because of no elasticity in the cuff.